Phytochemical, Pharmacological and Toxicological Aspects of Hibiscus sabdariffa L.: A Review
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PHYTOTHERAPY RESEARCH
Phytother. Res. 19, 369–375 (2005)
Published online in Wiley InterScience (www.interscience.wiley.com).
HIBISCUS SABDARIFFA DOI:
L. 10.1002/ptr.1628 369
REVIEW ARTICLE
Phytochemical, Pharmacological and
Toxicological Aspects of Hibiscus sabdariffa
L.: A Review
Badreldin H. Ali1, Naser Al Wabel1 and Gerald Blunden2*
1
Department of Veterinary Medicine, Al-Gaseem University, Buraydah, Al Gaseem 81999, Saudi Arabia
2
School of Pharmacy and Biomedical Sciences, University of Portsmouth, St Michael’s Building, White Swan Road, Portsmouth
PO1 2DT, UK
This article reviews the reported phytochemical, pharmacological and toxicological properties of Hibiscus
sabdariffa L. (English: roselle, red sorrel; Arabic: karkade), the calyces of which are used in many parts of the
world to make cold and hot drinks. Nutritionally, these contain ascorbic acid (vitamin C). In folk medicine, the
calyx extracts are used for the treatment of several complaints, including high blood pressure, liver diseases
and fever.
The pharmacological actions of the calyx extracts include strong in vitro and in vivo antioxidant activity.
In rats and rabbits, the extract showed antihypercholesterolaemic, antinociceptive and antipyretic, but not
antiinflammatory activities. In rat and man a strong antihypertensive action has been demonstrated. The
effects of the calyx extracts on smooth muscles in vitro are variable, but they mostly inhibit the tone of
the isolated muscles. In healthy men, consumption of H. sabdariffa has resulted in significant decreases in the
urinary concentrations of creatinine, uric acid, citrate, tartrate, calcium, sodium, potassium and phosphate, but
not oxalate. Oil extracted from the plant’s seeds has been shown to have an inhibitory effect on some bacteria
and fungi in vitro.
The plant extracts are characterized by a very low degree of toxicity. The LD50 of H. sabdariffa calyx extract
in rats was found to be above 5000 mg/kg. A single report has suggested that excessive doses for relatively
long periods could have a deleterious effect on the testes of rats.
In view of its reported nutritional and pharmacological properties and relative safety, H. sabdariffa and
compounds isolated from it (for example, anthocyanins and Hibiscus protocatechuic acid) could be a source
of therapeutically useful products. Copyright © 2005 John Wiley & Sons, Ltd.
Keywords: Hibiscus sabdariffa; antioxidant; anticancer; anthocyanins; Hibiscus protocatechuic acid; glycinebetaine.
INTRODUCTION CONSTITUENTS
Hibiscus sabdariffa L. (family Malvaceae), commonly There are many published reports on the constituents
known in English as roselle or red sorrel and in Arabic of different plant parts of H. sabdariffa, which have
as karkadeh, is widely grown in Central and West been summarized briefly by Ross (2003). Citric and
Africa, South East Asia, and elsewhere. The plant malic acids have been reported as the major organic
(family Malvaceae) is an erect annual herb, the botan- acids in aqueous extracts of the flowers by Buogo and
ical features of which have been described by Ross Picchinenna (1937), Indovina and Capotummino (1938)
(2003). The thick, red and fleshy, cup-shaped calyces of and Reaubourg and Monceaux (1940), but tartaric acid
the flower are consumed worldwide as a cold beverage was found only as a trace component by Indovina and
and as a hot drink (sour tea). These extracts are also Capotummino (1938), although it was detected, along
used in folk medicine against many complaints that with citric and oxalic acids, by paper chromatography
include high blood pressure, liver diseases and fever in flower extracts from Taiwan (Lin, 1975). Kerharo
(Dalziel, 1973; Wang et al., 2000; Ross, 2003). The red (1971) reported high concentrations of organic acids in
anthocyanin pigments in the calyces are used as food the calyx, with citric acid predominating, but with malic
colouring agents (Esselen and Sammy, 1975). and tartaric acids also present. Khafaga and Koch
The purpose of the present article is to gather (1980a) detected citric, hibiscus, malic and tartaric
together the available published information on the acids in the calyces of five strains of H. sabdariffa var.
constituents of the plant and its pharmacological and sabdariffa. In all strains, the concentration of acids in-
toxicological properties. creased during development of the calyces, but declined
after they reached ripeness. Ascorbic acid was reported
* Correspondence to: Professor G. Blunden, School of Pharmacy and
Biomedical Sciences, University of Portsmouth, St Michael’s Building,
in aqueous extracts by Buogo and Picchinenna (1937)
White Swan Road, Portsmouth PO1 2DT, UK. and Reaubourg and Monceaux (1940), but was not
E-mail: asmita.sautreau@port.ac.uk detected by Indovina and Capotummino (1938).
Copyright © 2005 John Wiley & Sons, Ltd. Phytother.Received
Res. 19,14 October(2005)
369–375 2004
Accepted 14 December 2004
Copyright © 2005 John Wiley & Sons, Ltd.370 B. H. ALI ET AL.
Figure 1. Chemical structures of some major constituents of Hibiscus sabdariffa flowers.
Most of the chemical investigations of the flower given. Gossypitrin had been shown earlier to be the
constituents have been directed towards characteriza- 7-glucoside of gossypetin (Figure 1, 5) (Rao and
tion of their pigments. Yamamoto and Oshima (1932) Seshadri, 1939). Hibiscitrin was proved later to be the
isolated an anthocyanin, to which they assigned the 3-monoglucoside of hibiscetin (Rao and Seshadri, 1948a,
structure, cyanidin-3-glucoside. Later, they changed b). In 1961, Seshadri and Thakur isolated gossytrin from
this to delphinidin-pentoside-glucoside (Yamamoto and the flower petals of H. sabdariffa, which they showed
Oshima, 1936). Delphinidin and cyanidin were reported to be gossypetin-3-glucoside. Subramanian and Nair
as constituents of plants grown in Trinidad (Forsyth (1972) reported the isolation of gossypetin-8-glucoside,
and Simmonds, 1954) and Seshadri and Thakur (1961) gossypetin-7-glucoside and gossypetin-3-glucoside from
isolated delphinidin-3-glucoxyloside (delphinidin-3- H. sabdariffa var. altissima. The 8-glucoside, gossypin,
sambubioside: Figure 1, 1), also known as hibiscin. had been first isolated from Gossypium indicum by
Shibata and Furukawa (1969) studied the pigments Neelakantam and Seshadri (1936).
of Taiwanese roselle and also reported the presence of Rao and Seshadri (1942a) showed that the content
delphinidin-3-sambubioside, along with small amounts of of flavonol glycosides in the calyces was very low and
delphinidin-3-monoglucoside, cyanidin-3-monoglucoside that these compounds were to be found primarily in
and delphinidin. The pigments of the calyces of plants the flower petals.
grown in Trinidad were examined by Du and Francis Milletti et al. (1959) examined extracts of H. sabdariffa
(1973), who also isolated delphinidin-3-sambubioside by paper chromatography and reported the detection
(major component), delphinidin-3-monoglucoside and of hibiscin, gossypetin, gossypetrin, quercetin, probably
cyanidin-3-monoglucoside, but, in addition, character- myricetin, hibiscetin, hibiscetrin, sabdaritrin, possibly
ized cyanidin-3-sambubioside (Figure 1, 2) as the second sabdaretin and an unidentified compound. Salah et al.
most abundant anthocyanin in the extract. Subramanian (2002), using TLC and HPLC fingerprint analysis of an
and Nair (1972) studied the pigments present in extract of H. sabdariffa flowers, showed the presence
H. sabdariffa var. altissima and reported the pre- of quercetin, luteolin, a luteolin glycoside and chloro-
sence of cyanidin-3, 5-diglucoside and cyanidin-3-(2G- genic acid, in addition to other compounds previously
glucosylrutinoside). Khafaga and Koch (1980b) reported recorded, such as the anthocyanins delphinidin-3-
the anthocyanins found in the calyces of five strains of sambubioside and cyanidin-3-sambubioside (Du and
H. sabdariffa var. sabdariffa. Cyanidin-3-sambubioside Francis, 1973), the flavonoids gossypetin, hibiscetin
was the major pigment, followed by cyanidin-3- and their respective glycosides (Subramanian and Nair,
glucoside. Delphinidin glycosides were lacking in the 1972), protocatechuic acid (Tseng et al., 1996), eugenol
Senegalese strain, but were present in the other four (Chen et al., 1998) and the sterols β -sitosterol and
strains. During calyx growth, the anthocyanin content ergosterol (Salama and Ibrahim, 1979). Quercetin had
reached 1.7% to 2.5% of the dry weight in all strains. also been recorded by Takeda and Yasui (1985) in
From the flowers of H. sabdariffa, Rao and Seshadri roselle colour.
(1942a) isolated the flavonol glycoside, hibiscitrin, Hibiscus protocatechuic acid (3, 4-dihydroxybenzoic
which on hydrolysis yielded the aglycone, hibiscetin acid; Figure 1, 3) was isolated from the dried flowers
(Figure 1, 4). In a further publication, Rao and Seshadri of H. sabdariffa and its structure elucidated by Tseng
(1942b) reported the isolation, from the flower petals et al. (1996).
of the same species, of hibiscitrin, gossypitrin and The seed oil of H. sabdariffa was analysed by Jirovetz
sabdaritrin. The last of these, on acid hydrolysis, yielded et al. (1992). More than 25 volatile compounds were
an hydroxyflavone to which the name sabdaretin was detected, mainly unsaturated hydrocarbons, alcohols
Copyright © 2005 John Wiley & Sons, Ltd. Phytother. Res. 19, 369–375 (2005)HIBISCUS SABDARIFFA L. 371
and aldehydes, predominantly from C8 to C13. Chen included rabbit aortic strip (Obiefuna et al., 1994)
et al. (1998) studied the composition of the volatile and rat ileal strip (Salah et al., 2002). The extract also
constituents of roselle tea. More than 37 compounds rhythmically contracted rat uterus, guinea-pig tracheal
were characterized, which were classified into four chain and rat diaphragm. The same extract stimulated
groups: fatty acid derivatives, sugar derivatives, phe- quiescent rat uterus and frog rectus abdominus muscle
nolic derivatives and terpenoids. Four differently treated (Sharaf, 1962; Ali et al., 1991). The tonic effects on rat
samples were analysed, untreated, frozen, hot air-dried uterus were partially reduced by hydrocortisone and
at 50 °C and hot air-dried at 75 °C. The volatile composi- indomethacin. The mechanism of action of H. sabdariffa
tion of each sample varied considerably, for example aqueous extract on smooth muscles is not certain. How-
significant amounts of furfural and 5-methyl-2-furfural ever, as the extracts contain organic acids and minerals
were found in the oven-dried samples, whereas only (for example, Reaubourg and Monceaux, 1940), the
minimal amounts were detected in the fresh and effect of the extract on different smooth muscle pre-
frozen samples. The major components of the fresh parations would be expected to be variable. The over-
sample were (Z)-3-hexenol, 2-hexenol and 1-hexenol, all effect is a direct relaxation of the smooth muscles,
whereas these were present either in small amounts or which may explain, at least partially, the hypotensive
were absent from the other samples. α-Terpineol was action of the extract (see below). It was suggested that
a major constituent of the fresh and frozen calyces, the relaxant response was related to endothelium-
whereas the yields from the oven-dried samples were dependent and endothelium-independent mechanisms
substantially lower. Eugenol was found in all four (Obiefuna et al., 1994), or mediated through calcium
samples in about similar amounts. channels, possibly generated by constituents such as
The petals of Hibiscus sabdariffa yielded 65% (dry quercetin and eugenol (Salah et al., 2002). However,
weight) of mucilage, which on hydrolysis yielded galac- the presence of stimulatory substance(s) in the extract
tose, galacturonic acid and rhamnose (El-Hamidi et al., has also been demonstrated using the frog rectus
1966). abdominus preparation (Ali et al., 1991). Further stud-
Three water-soluble polysaccharides have been ies of the mechanistic aspects of the extract on smooth
extracted from the flower buds of H. sabdariffa. The muscles are warranted.
neutral compounds are composed of arabinans and
arabinogalactans of low relative molecular mass. The
major fraction was shown to be a pectin-like molecule Effect on blood pressure
(Mr = 105 Da). The main chain is composed of α-1, 4-
linked galacturonic acid (24% methyl esterified) and α- Intravenous injection of aqueous extracts of H.
1, 2-linked rhamnose. Side chains are built of galactose sabdariffa calyx to anaesthetized cats (Ali et al., 1991)
and arabinose and are connected to the main chain via and anaesthetized rats (Adegunloye et al., 1996)
C-4 of every third rhamnose (Muller and Franz, 1992). lowered blood pressure in a dose-dependent manner.
The sterols of the seed oil of H. sabdariffa were This effect was resistant to a number of standard
studied by Salama and Ibrahim (1979), who reported receptor blocking agents, but the hypotensive effect was
the presence of cholesterol, campasterol, stigmasterol, partially blocked by atropine (Ali et al., 1991), and
β -sitosterol, α-spinasterol and ergosterol. atropine and antihistamine (H1 blockers) (Adegunloye
As glycinebetaine and trigonelline have been found et al., 1996). Therefore, the hypotensive action may
as constituents of the flowers of Hibiscus rosa-sinensis be mediated, at least partially, by a cholinergic and/or
L. (Blunden et al., 2001), their possible presence in the histaminergic mechanism. Sectioning of the left and right
calyces of H. sabdariffa was investigated. Two com- vagi nerves did not have a significant effect on the fall
mercial samples of roselle (Elnasr Hibiscus, Khartoum, in mean arterial blood pressure (Adegunloye et al.,
Sudan) were extracted and processed using the same 1996). It was also postulated that the hypotensive
procedures as those described by Blunden et al. (2001). action of H. sabdariffa could be ascribed to a direct
This entailed purification of each extract by passage vaso-relaxant effect (Adegunloye et al., 1996). Another
through a column of cation exchange resin, examina- possible mechanism for the hypotensive activity may
tion of the semi-purified extracts by two-way thin layer be inhibition of angiotensin I converting enzyme (ACE).
chromatography (TLC), isolation of the Dragendorff- The latter action has been demonstrated in vitro with a
positive compounds by preparative TLC, and identifica- crude hydroethanol extract of H. sabdariffa calyces,
tion of them by 1H-NMR spectroscopy (D2O; 400 MHz) and was ascribed to flavones present in the extract.
and fast atom bombardment mass spectrometry. The In addition, a beneficial cardioprotective effect of this
content of each betaine present in the original extracts extract was shown in vivo, and was attributed to
was determined using a 1H-NMR spectroscopic assay flavonoids and anthocyanins (Jonadet et al., 1990). More
(Blunden et al., 1986). Both glycinebetaine and trigonelline recently, the antihypertensive action of H. sabdariffa
were detected with yields (dry weight) of 0.7% and has been confirmed in rats with experimental hyper-
1.1% and 0.007% and 0.02%, respectively. tension (Odigie et al., 2003) and in spontaneously
hypertensive rats (Onyenekwe et al., 1999) given the
aqueous extracts at doses of 250–1000 mg/kg for up to
14 weeks.
PHARMACOLOGICAL PROPERTIES In a single clinical trial involving 54 patients with
moderate essential hypertension, Haji-Faraji and Haji-
Effect on smooth muscle Tarkhani (1999) have reported that daily consumption
of an aqueous H. sabdariffa extract (two spoonfuls
The aqueous extract of H. sabdariffa calyces inhibited of blended ‘sour tea’ boiled in one glass of water
the tone of various isolated muscle preparations that for 20–30 min) resulted in about an 11% decrease in
Copyright © 2005 John Wiley & Sons, Ltd. Phytother. Res. 19, 369–375 (2005)372 B. H. ALI ET AL.
systolic and diastolic blood pressure 12 days after (Tanaka et al., 1994), azoxymethane in the colon
beginning the treatment. Three days after cessation of (Kawamori et al., 1994), N-methyl-N-nitrosourea in
the treatment, the blood pressure rose again by about glandular stomach tissue (Tanaka et al., 1995) and N-
6–8%. The authors did not investigate the possible butyl-N-(4-hydroxybutyl)nitrosamine in the bladder
mechanism(s) of action of the plant extract, but a diu- (Hirose et al., 1995). Topical application of Hibiscus
retic, vasodilator and/or an inhibitory effect on ACE protocatechuic acid prior to treatment with 12-O-
was postulated. tetradecanoylphorbol-13-acetate to female mice, initi-
The effectiveness of an aqueous extract of H. ated with benzo[α]pyrene, inhibited the incidence of
sabdariffa on mild to moderate hypertension was re- tumours (Tseng et al., 1998). Tseng et al. (2000) also
cently confirmed in a clinical trial involving 39 Mexican demonstrated that Hibiscus protocatechuic acid inhib-
patients (Herrera-Arellano et al., 2004). The extract was its the survival of human promyelocytic HL-60 cells
made from 10 g dried calyx in 0.5 L water (9.6 mg in a concentration- and time-dependent manner. The
anthocyanin content) and was given daily for 4 weeks data presented by Tseng et al. (2000) suggest that the
before breakfast. For comparison, 36 hypertensive compound is an apoptosis inducer in human leukaemia
patients were given the ACE inhibitor, captopril cells and that RB phosphorylation and Bcl-2 protein
(25 mg twice daily for 4 weeks). The extract treatment may play a crucial role in the early stage.
reduced the systolic blood pressure from 139 to 124 mm Oxidation of low-density lipoprotein can increase
mercury, and the diastolic from 91 to 80 mm mercury. the incidence of atherosclerosis. Lee et al. (2002) have
These results were not significantly different from those reported that Hibiscus protocatechuic acid inhibits
obtained by captopril treatment. No adverse effects this oxidation induced by either copper or a nitric acid
were found with either treatment, confirming the donor.
effectiveness and safety of the extract. The anthocyanins of H. sabdariffa were also
shown to have a protective effect against tert-
butylhydroperoxide-induced hepatic toxicity in rats
Antioxidant and anticancer activity (Wang et al., 2000). The anthocyanins were able to
quench the free radicals of 1, 1-diphenyl-2-picrylhydrazyl
An 80% ethanol extract of H. sabdariffa was effec- and this antioxidant effect was also demonstrated by
tive in reducing about 60%–90% of the mutagenicity the ability of the anthocyanins to reduce the cytotoxicity
induced by heterocyclic amines at a concentration of induced by tert-butylhydroperoxide in rat primary
12.5 mg/plate in the salmonella mutation assay. Below hepatocytes and to attenuate hepatotoxicity in rats
this dose, neither significant antimutagenic nor anti- (Wang et al., 2000). Administration of the anthocyanins
bacterial effects were observed (Chewonarin et al., isolated from the plant (100 or 200 mg/kg/day for 5 days)
1999). The extract of the plant also inhibited the significantly reduced the activities of the serum enzymes
formation of colon cancer at the initiation stage. indicative of liver damage, ameliorated histological
Fractions of the ethanol extract of dried flowers of lesions and reduced oxidative liver damage. Similar
H. sabdariffa were evaluated by their capacity to quench dosages of H. sabdariffa anthocyanins were effective in
1, 1-diphenyl-2-picrrylhydrazyl free radical and inhibit- significantly mitigating the pathotoxicity induced by
ing xanthine oxidase activity. The ethyl acetate fraction paracetamol in mice (Ali et al., 2003). It has also been
of the ethanol extract showed the greatest ability of reported that anthocyanins protect against DNA dam-
scavenging free radical and the chloroform fraction age induced by tert-butylhydroperoxide in rat smooth
showed the strongest inhibitory effect on xanthine muscle and hepatoma cells (Lazze et al., 2003). In view
oxidase activity. The antioxidant activities of the vari- of the established strong antioxidant and antilipid
ous extracts were also investigated using a model of peroxidation actions of H. sabdariffa extracts and the
tert-butyl hydroperoxide-induced oxidative damage in compounds they contain (Tseng et al., 1997; Wang
rat primary hepatocytes. Both fractions were shown et al., 2000; Suboh et al., 2004), and because many dis-
to be active, indicating that the extract of dried H. eases and conditions (for example, diabetes and aging)
sabdariffa flowers protect rat hepatocytes from tert-butyl are thought to involve lipid peroxidation and the gen-
hydroperoxide-induced cytotoxicity and genotoxicity by eration of free radicals (Poon et al., 2004; Vincent et al.,
different mechanisms (Tseng et al., 1997). 2004), the anthocyanins (from this and other plants)
The calyces of H. sabdariffa contain anthocyanins and Hibiscus protocatechuic acid may potentially be
(for example, Shibata and Furukawa, 1969; Du and useful in ameliorating or preventing these diseases and
Francis, 1973) and Hibiscus protocatechuic acid (Tseng conditions.
et al., 1996). It was demonstrated that Hibiscus proto- Glycinebetaine has also been shown to protect against
catechuic acid has a protective effect against cytotoxicity hepatotoxicity induced by bacterial lipopolysaccharides
and genotoxicity induced by tert-butylhydroperoxide in (Kim and Kim, 2002), by ethanol (Kanbak et al., 2001),
a primary culture of rat hepatocytes (Tseng et al., 1996) niacin therapy (McCarty, 2000), chloroform (Kim and
and it was proposed that one of the mechanisms of this Kim, 1998) and methotrexate (Barak et al., 1984).
protective effect was associated with the scavenging of Glycinebetaine in extracts of Hibiscus calyces could,
free radicals. Hibiscus protocatechuic acid also inhibits therefore, have a significant therapeutic role.
lipopolysaccharide-induced rat hepatic damage (Lin
et al., 2003) and tert-butylhydroperoxide-induced rat
hepatotoxicity (Liu et al., 2002). Hibiscus protocatechuic Antipyretic, antinociceptive and antiinflammatory
acid has also been shown to inhibit the carcinogenic activities
action of various chemicals in different tissues of the
rat, including diethylnitrosamine in the liver (Taneka Dafallah and Al-Mustafa (1996) have reported that, in
et al., 1993), 4-nitroquinoline-1-oxide in the oral cavity rats, an aqueous extract of H. sabdariffa was effective
Copyright © 2005 John Wiley & Sons, Ltd. Phytother. Res. 19, 369–375 (2005)HIBISCUS SABDARIFFA L. 373
in inhibiting yeast-induced pyrexia, and in reducing the migration and calcification in the blood vessel of treated
reaction time in a hot plate, tail-flick assay, indicating rabbits (Chen et al., 2003).
that the extract has antipyretic and antinociceptive
actions. The extract, however, was without significant
effect in the rat paw carrageenan-induced oedema Antibacterial, antifungal and antiparasitic actions
test (Dafallah and Al-Mustafa, 1996), which is one
marker used for assaying antiinflammatory action. Oil extracted from seeds of H. sabdariffa has been
However, in one clinical trial involving 50 patients, shown to have an in vitro inhibitory effect on Bacillus
administration of a decoction of dried fruit (3 g/person, anthracis and Staphylococcus albus, but not Proteus
three times every day for 7 days to 1 year) was shown vulgaris and Pseudomonas aeruginosa (Gangrade et al.,
to produce antiinflammatory activity (Anon, cited in 1979). An ethanol extract of the dried leaves of the
Ross, 2003). More work on this aspect, using several plant has been shown to reduce aflatoxin forma-
models for the assay of antiinflammatory activity is tion (El-Shayeb and Mabrook, 1984), and to have an
warranted. It was suggested that the above antipyretic in vitro inhibitory effect against some fungi that
and antinociceptive actions could be attributed to include Aspergillus fumigatus, Rhizopus nigricans and
flavonoids, polysaccharides and organic acids (Dafallah Trichophyton mentagrophytes (Guerin and Reveillere,
and Al-Mustafa, 1996). Further work is required to 1984). An ethanol extract of the dried leaves was found
study the effects of fractions and isolated compounds to be ineffective against Lumbricus terrestris (Boum
in experimental antiinflammatory, antipyretic and anti- et al., 1985).
nociceptive tests and their possible mechanism(s) of An aqueous extract of dried sepals of H.
action. sabdariffa (100 ppm) was active against Schistosoma
mansoni. However, an aqueous extract of dried
seeds (10 000 ppm) was inactive against this trematode
Renal effects (Elsheikh et al., 1990).
Workers studied, in six normal Thai subjects, the
changes in urine composition that follow the consump- Interaction with drugs
tion of H. sabdariffa extract at different concentrations
and for various periods of time (Kirdpon et al., 1994). The interaction of three Sudanese beverages, includ-
This work indicated that consumption of H. sabdariffa ing H. sabdariffa, with the kinetics of chloroquine was
extract resulted in significant decreases in the urinary studied in human volunteers (Mahmoud et al., 1994).
concentrations of creatinine, uric acid, citrate, tartrate, H. sabdariffa was found not to have a significant effect
calcium, sodium, potassium and phosphate, but not on any pharmacokinetic parameter, indicating its safety
oxalate. It was noted that the low dose of H. sabdariffa when taken with drugs that may have the metabolic
(16 g/day) caused a more significant decrease in salt pathways of chloroquine. More recently, Kolawole and
output in the urine than a high dose (24 g/day). A Maduenyi (2004) studied the effect of H. sabdariffa
significant uricosuric action was noted in rats given a water extract on paracetamol (acetaminophen) kinetics
decoction of the dried calyx at an oral dose of 1 g/kg in healthy men. On the whole, the administration of
(Caceres et al., 1987; Mojiminiyi et al., 2000). the extract induced no significant changes in the major
kinetic parameters of paracetamol, although very
minor and probably biologically insignificant alterations
Anticholesterol effects in some were observed. In view of the fact that H.
sabdariffa drinks may be ingested with medicines, more
H. sabdariffa calyx (5% or 10%) was fed to rats with studies to ascertain the presence or absence of inter-
hypercholesterolaemia for 9 weeks (El-Saadany et al., actions with drugs of different metabolic profiles are
1991). The treatment progressively lowered the differ- warranted.
ent lipid fractions in plasma, heart, brain, kidney and
liver; and also decreased the activities of several plasma
enzymes used in tests as markers of tissue function. Toxicological properties
This treatment, however, slightly raised the content of
plasma phospholipids. Although the mechanism of ac- The LD50 of H. sabdariffa calyx extract in rats was
tion of H. sabdariffa as a cholesterol-lowering agent found to be above 5000 mg/kg (Onyenekwe et al., 1999),
was not elucidated in this work, it was hypothesized, suggesting that the extract is virtually non-toxic. In
albeit with no experimental evidence, that the extract spontaneously hypertensive rats, treatment with the
may contain some compounds that activate hormonal extract at doses of 500–1000 mg/kg decreased blood
secretions, such as adrenocortical hormones, which pressure, and also significantly decreased serum
stimulate the metabolic pathway of cholesterol by creatinine, cholesterol and glucose levels, but signific-
conversion into other compounds. antly increased the serum content of uric acid. The
The anticholesterol action of H. sabdariffa (0.5% or treatment caused no significant effect on either water
1%) was confirmed in rabbits fed cholesterol for 10 intake or urine output.
weeks. This treatment was effective in reducing the Workers from Nigeria have recently studied the ef-
serum concentrations of triglycerides, total cholesterol fect of sub-chronic administration of aqueous extracts
and low-density lipoprotein cholesterol, and in mitigat- of H. sabdariffa calyx on the testes (Orisakwe et al.,
ing atherosclerosis in the aorta. Histopathologically, 2004), as the plant is often claimed in West African
it was found that feeding H. sabdariffa had reduced folk medicine to be an aphrodisiac (Dalziel, 1973;
foam cell formation and inhibited smooth muscle cell Orisakwe et al., 2004). Rats were given 1.15, 2.3 and
Copyright © 2005 John Wiley & Sons, Ltd. Phytother. Res. 19, 369–375 (2005)374 B. H. ALI ET AL.
4.6 g/kg/day of an aqueous extract of H. sabdariffa of the testicular toxicity of H. sabdariffa in humans is
calyx in the drinking water for up to 12 weeks. At not certain when the relatively high amount of extract
the end of the treatment period there was a steady given in the drinking water for 12 weeks is taken into
decrease in body weight, but no changes in the relative consideration.
or absolute weights of the testes. However, the higher Akindahunsi and Olaleye (2003) suggested that, in
two doses of the extract caused a significant decrease rats, the average consumption of 150–180 mg/kg/day of
in the epididymal sperm counts, histological distortion an aqueous-ethanol extract of H. sabdariffa calyces
of tubules, disruption of normal testicular epithelial appeared to be safe, although higher doses might elevate
organization and disintegration of sperm cells. The the activity of some plasma enzymes indicative of
authors postulated that these effects were related to tissue function (such as alanine aminotransferase and
interference by the extract with spermatogenesis that aspartate aminotransferase). However, the activity of
may have been caused by an oestrogenic action of some related plasma enzymes (alkaline phosphatase and
the extract. Indeed, Ali et al. (1989) have previously lactate dehydrogenase) was not significantly affected,
alluded to this possibility. It is, however, difficult to nor was there any evidence of histological damage to
ascribe the above testicular effects to an oestrogenic the heart and liver of the treated rats.
action in the absence of any significant change in tes- Mutagenicity of roselle colour was reported by
ticular weight, as oestrogens are known to reduce the Takeda and Yasui (1985) and the compound respon-
weights of the male reproductive organs. The relevance sible for this activity was suggested to be quercetin.
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